In general, a reciprocating compressor is designed to form a compression space to/from which an operation gas is sucked/discharged between a piston and a cylinder, and the piston linearly reciprocates inside the cylinder to compress refrigerants.
Most reciprocating compressors today have a component like a crankshaft to convert a rotation force of a drive motor into a linear reciprocating drive force for the piston, but a problem arises in a great mechanical loss by such motion conversion. To solve the problem, development of linear compressors is still under progress.
Linear compressors have a piston that is connected directly to a linearly reciprocating linear motor, so there is no mechanical loss by the motion conversion, thereby not only enhancing compression efficiency but also simplifying the overall structure. Moreover, since their operation is controlled by controlling an input power to a linear motor, they are much less noisy as compared to other compressors, which is why linear compressors are widely used in indoor home appliances such as a refrigerator.
FIG. 1 illustrates one example of a linear compressor in accordance with a prior art.
The conventional linear compressor has an elastically supported structure inside a shell (not shown), the structure including a frame 1, a cylinder 2, a piston 3, a suction valve 4, a discharge valve assembly 5, a motor cover 6, a supporter 7, a back cover 8, mainsprings S1 and S2, a muffler assembly 9, and a linear motor 10.
The cylinder 2 is insertedly fixed to the frame 1, and the discharge assembly 5 constituted by a discharge valve 5a, a discharge cap 5b, and a discharge valve spring 5c is installed to cover one end of the cylinder 2. The piston 3 is inserted into the cylinder 2, and the suction valve 4 which is very thin is installed to open or close a suction port 3a of the piston 2.
The motor cover 6 supports an outer stator 12 of the linear motor 10 in an axial direction to fix the outer stator 12 and is bolted to the frame 1 at the same time. The back cover 8 is coupled to the motor cover 6, and between the motor cover 6 and the back cover 8 there is the supporter 7 that is connected to the other end of the piston 3, while being elastically supported in an axial direction by the mainsprings S1 and S2. The muffler assembly 9 for sucking in refrigerant is also fastened to the supporter 7.
Here, the mainsprings S1 and S2 consist of four front springs S1 and four rear springs S2 that are arranged horizontally and vertically symmetrical about the supporter 7. As the linear motor 10 starts running, the front springs S1 and the rear springs S2 move in opposite directions and buff the piston 3 and the supporter 7. In addition to these springs, the refrigerant in the compression space P functions as sort of a gas spring to buff the piston 3 and the supporter 7.
The linear motor 10 includes an inner stator 11, an outer stator 12, a permanent magnet 13, and a connecting member 14, and is installed in such a way that the permanent magnet 13 is able to linearly reciprocate while maintaining an air-gap between the inner stator 11 and the outer stator 12. The permanent magnet 13 is operationally connected to the piston 3 with a connecting member 14. Because of that, when the permanent magnet 13 makes a linear reciprocating motion by an interactive electromagnetic force between itself and the inner and outer stators 11 and 12, it causes the piston 3 to move as well.
Therefore, when the linear motor 10 starts running, the piston 3 and the muffler assembly 9 connected to the piston 3 linearly reciprocate together, and with variations in pressure of the compression space P the operation of the suction valve 4 and the discharge valve assembly 5 are automatically regulated. Through this operation mechanism, refrigerant is sucked into the compression space P after travelling through the suction pipe on the side of the shell, the opening in the back cover 9, the muffler assembly 10, and the suction ports 3a in the piston, is compressed, and then escapes to the outside via the discharge cap 5b, a loop pipe L, and an outflow pipe on the side of the shell.
FIG. 2 illustrates one example of an outer stator in a linear compressor in accordance with a prior art. The conventional outer stator 12 is constituted by a coil 12a wound around a bobbin (not shown) in a circumference direction to enable the current flow, a plurality of core blocks 12b arranged in a circumference direction at predetermined intervals, and injection-molded bodies 12c for securing the core blocks 12b to the coil 12a. 
To obtain the outer stator, one winds the coil 12a around the bobbin, tentatively arranges the core blocks 12b in the circumference direction of the coil 12a at predetermined intervals using the a jig (not shown), and secures the core blocks 12b at the coil 12a through insert injection. At this time, insulation between the coil 12a and the core blocks 12b should be performed in order to prevent the current flow between them. This is achieved by filling a space between the coil 12a and the core blocks 12b with the injection-molded bodies 12c, or by making sure that the core 12a and the core blocks 12b are spaced apart from each other by a certain distance.
In the former case, however, where insulation between the coil and the core blocks is performed with use of the injection-molded bodies, it is difficult to check whether the space is filled with the injection-molded bodies in a satisfactory manner, and this difficulty is often led to deterioration in the performance reliability, increase in production cost, and possible deformation after the injection-molded bodies are hardened, thereby requiring a post-process to ensure an air-gap between the inner stator, the outer stator, and the permanent magnet later, not being advantageous in terms of mass productivity.
On the other hand, in the case that the coil and the core blocks are spaced apart from each other by a certain distance for insulation, an overall size of the linear motor increases and further the linear compressor using such a motor increases in size also.